/*
 * Copyright (C) 2009 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect;

import com.google.common.annotations.GwtCompatible;
import com.google.errorprone.annotations.concurrent.LazyInit;

import java.io.Serializable;
import java.util.Collection;
import java.util.EnumSet;
import javax.annotation.CheckForNull;

/**
 * Implementation of {@link ImmutableSet} backed by a non-empty {@link java.util.EnumSet}.
 *
 * @author Jared Levy
 */
@GwtCompatible(serializable = true, emulated = true)
@SuppressWarnings("serial") // we're overriding default serialization
@ElementTypesAreNonnullByDefault
final class ImmutableEnumSet<E extends Enum<E>> extends ImmutableSet<E>
{
    @SuppressWarnings("rawtypes") // necessary to compile against Java 8
    static ImmutableSet asImmutable(EnumSet set)
    {
        switch (set.size())
        {
            case 0:
                return ImmutableSet.of();
            case 1:
                return ImmutableSet.of(Iterables.getOnlyElement(set));
            default:
                return new ImmutableEnumSet(set);
        }
    }

    /*
     * Notes on EnumSet and <E extends Enum<E>>:
     *
     * This class isn't an arbitrary ForwardingImmutableSet because we need to
     * know that calling {@code clone()} during deserialization will return an
     * object that no one else has a reference to, allowing us to guarantee
     * immutability. Hence, we support only {@link EnumSet}.
     */
    private final transient EnumSet<E> delegate;

    private ImmutableEnumSet(EnumSet<E> delegate)
    {
        this.delegate = delegate;
    }

    @Override
    boolean isPartialView()
    {
        return false;
    }

    @Override
    public UnmodifiableIterator<E> iterator()
    {
        return Iterators.unmodifiableIterator(delegate.iterator());
    }

    @Override
    public int size()
    {
        return delegate.size();
    }

    @Override
    public boolean contains(@CheckForNull Object object)
    {
        return delegate.contains(object);
    }

    @Override
    public boolean containsAll(Collection<?> collection)
    {
        if (collection instanceof ImmutableEnumSet<?>)
        {
            collection = ((ImmutableEnumSet<?>) collection).delegate;
        }
        return delegate.containsAll(collection);
    }

    @Override
    public boolean isEmpty()
    {
        return delegate.isEmpty();
    }

    @Override
    public boolean equals(@CheckForNull Object object)
    {
        if (object == this)
        {
            return true;
        }
        if (object instanceof ImmutableEnumSet)
        {
            object = ((ImmutableEnumSet<?>) object).delegate;
        }
        return delegate.equals(object);
    }

    @Override
    boolean isHashCodeFast()
    {
        return true;
    }

    @LazyInit
    private transient int hashCode;

    @Override
    public int hashCode()
    {
        int result = hashCode;
        return (result == 0) ? hashCode = delegate.hashCode() : result;
    }

    @Override
    public String toString()
    {
        return delegate.toString();
    }

    // All callers of the constructor are restricted to <E extends Enum<E>>.
    @Override
    Object writeReplace()
    {
        return new EnumSerializedForm<E>(delegate);
    }

    /*
     * This class is used to serialize ImmutableEnumSet instances.
     */
    private static class EnumSerializedForm<E extends Enum<E>> implements Serializable
    {
        final EnumSet<E> delegate;

        EnumSerializedForm(EnumSet<E> delegate)
        {
            this.delegate = delegate;
        }

        Object readResolve()
        {
            // EJ2 #76: Write readObject() methods defensively.
            return new ImmutableEnumSet<E>(delegate.clone());
        }

        private static final long serialVersionUID = 0;
    }
}
